Electrolytic process for the manufacture of hydrazine



y 1966 B. J. MAYLAND ETAL 3,251,755

ELECTROLYTIC PROCESS FOR THE MANUFACTURE OF HYDRAZINE Filed Aug. 16, 1962 ATTORNEYS BERTRAND Jv MAYLAND AND CHARLES 5. BRANDON,

23 INVENTOR.

Wfimw m FIG. 2

i of hydrazine is the Raschig process.

United States Patent M 3,251,755 ELECTROLYTIC PROCESS FOR THE MANUFAC- TURE 0F HYDRAZINE Bertrand J. Mayland, Jelfersoutown, and Charles S.

Brandon, Louisville, Ky., assignors to Girdler Corporation, Louisville, Ky., a corporation of Ohio Filed Aug. 16, 1962, Ser. No. 217,420 12 Claims. -(Cl. 204-101) The invention relates to the manufacture of hydrazine, and more particularly to an improved process and apparatus for the production of this compound.

Since it was first synthesized and isolated in 1887, the chemistry and utilization of hydrazine has been extensively studied. Recently, this compound has assumed a considerable importance as a rocket fuel and a chemical intermediate.

To date, the best method for commercial production In accordance with this method, hydrazine is manufactured by the controlled oxidation of ammonia or urea, carried out in an aqueous phase using sodium hypochlorite as an oxidizing agent. The reaction can be represented as follows:

The cost of hydrazine production by this method is high, due not only to the cost of the raw materials involved, but also to the inefficiency of the process. This inetficiency arises largely from undesirable side reactions such as:

Hydrazine is normally more reactive than ammonia, and some means of stopping the reaction of hydrazine is required to obtain a reasonable process efliciency. To this end, gelatine and animal glue have been used commercially with some degree of success but have not solved the essential problem. It has been suggested that hydrazine be made by electrolytic processes, but this has not solved the problem of side reactions and loss of product which has been set forth above.

It is an object of the present invention to provide a method and apparatus for producing hydrazine which will enable proper control of operating conditions to bring about a greater product yield with a greater efficiency than heretofore possible.

It is therefore the primary object of the preesnt invention to provide a method and apparatus for the production of hydrazine electrolytically in significant quantities.

These and other objects of the invention which will 'be understood by one skilled in the art upon reading the specifications, or which will be described hereinafter, are accomplished by that method and apparatus of which exemplary embodiments .will now be described. Reference is made to the accompanying drawings wherein:

Fig 1 is a typical flow diagram of the process of. the present invention.

FIG. 2 is a flow diagram of the invention as a continuous process.

Briefly in the practice of the invention electrolysis is employed, but it is employed in such a way as to limit the reaction to the anode and to avoid the reduction of the product which would otherwise tend to occur as the cathode. This is a ccomplished by the use of electrodialysis, with the division of the electrolytic cell into two or more parts in which different reactions occur.

Considering first FIG. 1, there is shown an electrolytic cell 1 provided with a cathode 2 and an anode 3. The electrolytic cell may be made of a glass, ceramic, inert 3,251,755 Patented May 17, 1966 plastic material, metal covered with rubber or plastic material, and the like. The cell is divided into two compartments marked respectively 4 and 5 by an anion membrane 6. It will be understood by those skilled in the art that an anion membrane includes a previous support covered with an anion exchange resin to the extent of being rendered impervious to liquid. Anion exchange resins are generally in the free base (sometimes called bydroxy form, an example of which is chloromethylated styrene divinyl benzene copolymer, aminated with trimethylamine. Amberlite IR410, Amberlite IR-40l, Amberlite IR-45, Amberlite IR-400, and Amberlite IRA- 410 are trademarks for resins of this class, made and sold by Rohm and Haas Company, and are suitable anion resins.

Assume that the compartment 5 of the electrolytic cell is filled with a solution of sodium chloride and that compartment 4 initially contains a water solution of ammonia and some ammonium chloride. Assume also that the anode and cathode are connected respectively to the poles of a source of unidirectional electric current. The bydroxyl ion will migrate through the anion membrane by a process of ion exchange and will seek the anode 3 where they will be discharged releasing nascent oxygen. This nascent oxygen is strongly oxidative in character, will tend to oxidize some of the ammonia to hydrazine, and will tend also to oxidize some of the chloride ions to hypochlorite ions. The further reaction of ammoniawith hypochlorite ions will tend to produce additional hydrazine. Additional hypochlorite ions will be formed by reaction with water of nascent chlorine formed by the discharge of chloride ions. Gas liberated at the anode is mainly O and C1 On the other hand hydrogen ions will migrate to the cathode 2 where they will be released. These ions are reducing in character, but by reason of the segregation of the two solutions in the cell, the hydrogen ions cannot serve to reduce the hydrazine. Hence the hydrogen is evolved as a gas at the cathode as indicated at 7 and can be vented from the system.

Ithas been found that an inhibitor in the compartment 4 is advisable to prevent the side reactions above described. The term inhibitor is intended to embrace materials such as animal glue, gelatin and chelating agents. There are various forms of chelating agents which may be employed, and their immediate efli'ect is that of complexing with polyvalent metallic ions in aqueous solutions. For example, various sodium salts of ethylenediaminetetraacetic acid are manufactured and sold by Dow Chemical Company under the trademark Versene and will serve the purpose very well.

. EXAMPLE I At the start of an electrodialysis operation compartment 5 of the cell of FIG. 1 contained a 1.0% solution of sodium chloride. Compartment 4 was filled with a water solution containing 20% ammonia, 1.0% ammonium chloride and 0.05% inhibitor. It was found that the current density could be considerably varied. In the particular instance it was 4 to 6 amperes/sq. ft. Electrolysis was continued for thirty minutes, the level of the water in the compartment 5 being made up as required at 8. At the end of the electrolysis the solution in the compartment 4 contained about .015 hydrazine. This solution was withdrawnthrough a conduit 9 and carried to a stripping tower 10. It was heated in the stripping tower by means of a steam coil 11. Free amonium was carried by means of a conduit 12 to a scrubber 13 wherein it was treated with water entering at 14 to provide an aqueous ammonia solution.

. Any free nitrogen or other insoluble gas was vented as tion of free amonia, was withdrawn through a conduit 16 and carried to a still (not shown). The solution was a solution containing mainly ammonium chloride and hydrazine. Upon distillation, a product consisting of hydrazine and water was driven off and condensed. As will be understood by the skilled worker in the art this mixture is non-explosive. Further dehydration of the hydrazine is accomplished by distillation. Concentration up to 1:1 molar ratio can be obtained by this means. If anhydrous hydrazine is required resort is had to chemical treatments, such as the addition of lime or other water absorbing materials.

The salt solution residue from the still can be discarded or treated with sodium hydroxide generated in compartment 5 to spring the amomnia to the chloride ion for recycle to compartment 4, or returned as an ammonium chloride salt solution for recycle to compartment 4. Likewise the solution of ammonia derived from the scrubber 13 may be returned to compartment 4 through a conduit 17 shown as having an inlet 18 for the addition of inhibitor and an inlet 19 for aqueous ammonium chloride solution.

The process described in connection with FIG. 1 is a batch process; but it serves to illustrate basic principles of operation underlying the invention. It was found possible to produce and recover hydrazine under the described conditions at a power consumption of about 10,000 coulombs per grain of hydrazine.

In order to improve the rate of formation of hydrazine in the anode chamber, hypochlorite ions are introduced in the cycle. In FIG. 1, this can be done by absorbing the chlorine liberated at the anode in the sodium hydroxide generated in the cathode chamber. The (0C1)- ion formed will then pass through the anion membrane to react with ammonia forming hydrazine by the Raschig reaction throughout the volume of the anode chamber in addition to the reaction at the anode surface.

Table I below illustrates the effects of different conditions obtaining during electrolysis, and the right hand column shows the ratios of hydrazine produced in the several operations.

Table I. Hydrazine production by elecirodialysz's [Effect of additives and chloride ions, 25% by wt. NHs

FIG. 2 illustrates in a diagrammatic fashion a continuous process for the production of hydrazine. Again there is an electrolytic cell 20 having a cathode 21 and an anode 22. This cell is shown as divided into compartments 23, 24 and 25 by means of ion exchange membranes 26 and 27. The membrane 26 is formed from a cation exchange resin. Cation resins are generally in a form which may be written RSO H, an example being a sulfonated divinyl benzene copolymer. Resins of this class are sold by the same company (Rohm and Hass Company) under trademarks such as Amberlite IR-l20, Amberlite IR-122, Amberlite IR-124 and Amberlite IRC-50.

'lytic cell.

The electrodes 21 and 22 are made of carbon or other inert electrical conductor. While they may under some circumstances may be made of metal, it is'well to avoid the use of metallic substances which would contaminate the electrolyte with extraneous metallic ions;

The first compartment 23 will contain a solution initially of sodium hydroxide; and during the electrolysis 'as above described, hydrogen will be evolved as at 28.

Solution from the compartment 23 may be continuously carried by a conduit 29 to a sodium hypochlorite generator 30, where the solution is continuously brought into contact with chlorine from a source hereinafter described. The solution of sodium hypochlorite is delivered from the generator by means of a pump 32 land a conduit 33 to the central compartment 24 of the electro- The conduit 33 is shown as having an inlet 34 for makeup of sodium chloride in aqeuous solution, or makeup water.

The diagrammatic representation of a conduit 35 indictates that overflow from the center cell compartment 24 is carried to the compartment 23.

The third cell compartment 25 receives from a conduit 37 an aqueous solution of ammonia from a source hereinafter described. The electrolytic action in the cell compartment 25 is such as to oxidize ammonia directly to hydrazine with the evolution of nascent gaseous chlorine and oxygen at the anode. Chlorine and oxygen are not vented, but instead are carried by a conduit 38 to the sodium hypochlorite generator 30.

The solution from the cell compartment 25, which is] primarily a solution of hydrazine, ammonia and chloride in water containing a small amount of inhibitor, is carried by a conduit 39 to an ammonia stripper. 40in the form of a tower containing bubble plates or Raschig rings. Here the solution is heated by means of a steam coil 41 so as to drive ofi the ammonia. The ammonia passes through a conduit 42 to a condenser 43 where it is dissolved in water. Provision is made for the addition of makeup ammonia at 44. From the condenser the ammonia passes to a storage tank 45 whence it may be pumped by a pump 46 through the conduit 37 so as to be is shown as having an inlet 47 for makeup inhibitor.

The stripped solution from the bottom of the tower 40 goes through a conduit 48 to a still 49 wherein it is fractionated to remove additional ammonia and water overhead. Vapor eflzluent from the still may. be returned through a conduit 51 to the stripper 40.

The crude concentrate in conduit 53 containing hydrazine and ammonium chloride in water is treated conventionally to recover NH Cl for recycle and hydrazinewater for further concentration. This is done by continuous evaporation taking the water-hydrazine overhead and continuous removal of NH Cl by cooling, crystallization or settling.

In the operation of this process and apparatus, hydrazine is formed throughout the volume of the anode chamber by oxidation of the ammonium'by (OCl)- ions-transported into chamber 25 through anion membrane 27,and

also at the anode surface by the action of .nascent oxygen and chlorine. Sodium from the center cell compartment 24 passes through the cation membrane 26 to the cathode compartment wherein sodium hydroxide is generated. In addition to (OCl) ions, chloride as well as hydroxyl ions are transferred through the anion membrane to oxidize ammonia to hydrazine in the ways set forth.

EXAMPLE II .5 chlorite and .05% sodium hydroxide. The solution in compartment 25 contained 20% ammonia, .2% hydrazine and about 0.1% inhibitor consisting of Versene, glue or gelatin or mixtures thereof.

The electrolysis can be carried on at room temperature although a somewhat elevated temperature and pressure may be used if desired. However, it is not generally practicable to allow the temperature to rise substantially above 200 F. by reason of the ion exchange membranes which may become undul'y softened. In the place of ion exchange membranes as hereinabove described, masses of ion exchange resins between foraminous supports can be used.

In the above example the current density was 4 to 6 amperes/sq. ft. and the concentration of hydrazine was 0.5%.

Modifications may be made in the invention without departing from the spirit of it. For example, with pressure operation higher ammonia concentrations can be used and higher hydrazine concentrations will be obtained. The invention having been described in certain exemplary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. A process of making hydrazine by the oxidation of ammonia, including the step of electrolyzing a water solution containing ammonium ions and chloride ions in an apparatus having an anode and a cathode in such fashion as to cause hydrogen ions to migrate to the cathode and hydroxyl ions to migrate to the anode while isolating the anode from the cathode by means of an anion exchange membrane whereby to prevent hydrogen released at the cathode from reacting with hydrazine formed at the anode.

2. The process claimed in claim 1 wherein the anion exchange membrane divides the electrolyte into two parts, the part adjacent the cathode consisting substantially entirely of a water solution of an alkali metal hydroxide and chloride, and the part adjacent the anode containing ammonium hydroxide.

3. The process claimed in claim 2 wherein the part of the electrolyte adjacent the anode contains also ammonium chloride.

4. The process claimed in claim 3 wherein a small quantity of a material chosen from a class consisting of glue, gelatin and chelating substances is added to the portion of the electrolyte adjacent the anode.

5. The process claimedin claim 4 wherein the portio of the electrolyte adjacent the anode is withdrawn and is treated with heat for the removal of free ammonia therefrom, the residual electrolyte being thereafter subjected to distillation, and the ammonia being returned to the electrolyte apparatus.

6. A process of making hydrazine by the oxidation of ammonia, wherein a water solution containing ammoni-- um ions is electrolyzed adjacent an anode in an electrolytic cell having a cathode and an anode and electrolytes, the cell being divided into a cathode compartment, an

anode compartment and an intermediate compartment disposed between the cathode compartment and the anode compartment, a cation permselective membrane separating said cathode and intermediate compartments and an anion permselective membrane separating said anode and intermediate compartments, there being in said cathode compartment a solution of a hydroxide of an alkali metal, in said intermediate compartment a solution of an alkali metal chloride and an alkali metal hypochlorite, and in said anode compartment a solution of ammonium hydroxide, ammonium chloride and hydrazine, whereby to evolve gaseous hydrogen in the cathode compartment adjacent the cathode, and chlorine in the anode compartment, the anode compartment adjacent the anode being kept free from hydrogen which would exert a reducing effect on the hydrazine therein. I

7. The process claimed in claim 6 wherein electrolyte is withdrawn from the cathode compartment and used to absorb said chlorine and returned to the intermediate compartment, the said chlorine being derived from the electrolysis in the anode compartment.

8. The process claimed in claim 7 wherein surplus electrolyte from the intermediate compartment is transferred to the cathode compartment.

9. The process claimed in claim 8 wherein electrolyte is withdrawn from the anode compartment and subjected to heat for the stripping of ammonia therefrom, the said ammonia after solution in water being returned to the anode compartment.

10. The process claimed in claim 9 wherein the stripped electrolyte is subjected to distillation, whereby to separate from said stripped electrolyte additional ammonia and a portion of water vapor leaving a crude concentrate containing hydrazine and ammonium chloride in water. 35

References Cited by the Examiner UNITED STATES PATENTS 2,813,067 11/1957 Stuart 20459 2,841,543 7/1958 Haller 204-59 2,978,393 4/1961 Hoch et al. 204-98 3,034,861 5/1962 Pursley 20459 JOHN H. MACK, Primary Examiner.

MURRAY TlLLMAN, Examiner.

L. G. WISE, H. FLOURNOY, Assistant Examiners. 

1. A PROCESS OF MAKING HYDRAZINE BY THE OXIDATION OF AMMONIA, INCLUDING THE STEP OF ELECTROLYZING A WATER SOLUTION CONTAINING AMMONIUM IONS AND CHLORIDE IONS IN AN APPARATUS HAVING AN ANODE AND A CATHODE IN SUCH FASHION AS TO CAUSE HYDROGEN IONS TO MIGRATE TO THE CATHODE AND HYDROXYL IONS TO MIGRATE TO THE ANODE WHILE ISOLATING THE ANODE FROM THE CATHODE BY MEANS OF AN ANION EXCHANGE MEMBRANE WHEREBY TO PREVENT HYDROGEN RELEASED AT THE CATHODE FROM REACTING WITH HYDRAZINE FORMED AT THE ANODE. 